This invention relates generally to sonic alarm devices and more particularly to a sonic alarm device adapted for a person with high frequency hearing impairment.
A large percentage of the population, especially older people, suffer impaired hearing of sounds in the high frequency part of the normal frequency range of audible hearing. A great many electronic alarm devices and warning devices emit periodic high frequency pulses. Usually these beeping sounds are generated by piezoelectric crystals. Unfortunately, these high frequency periodic beeps cannot be heard by people with high frequency hearing loss. Examples of such devices are smoke alarms, electric alarm clocks, alarm wristwatches, and some types of telephone annunciators.
Hearing devices have been disclosed in the prior art which separate the received sounds into frequency ranges and then treat the frequency bands separately. Hearing devices have primarily concentrated upon restoring a full range of frequencies, using well-known electronic techniques such as filters, compression, AGC etc. in an effort to provide normal hearing perception to the hearing impaired. An excellent catalog of this prior art is provided in U.S. Pat. No. 5,500,902, issued Mar. 19, 1996 to Stockham et al. These devices are very expensive and while they duplicate normal hearing while being worn, they are normally not worn during sleeping. Failure to hear an electronic alarm clock or a smoke alarm could be inconvenient or perhaps fatal.
U.S. Pat. No. 5,666,331 issued Sep. 9, 1997 to Kollin discloses an alarm clock for a hearing impaired person, in which a remote device responsive to audible alarm sounds generates carrier signals over the electrical power lines supplying power to an alarm clock, which cause a vibrator, lamp or sound device to pulse in synchronization with the power line frequency. This device is dependent upon the electric power lines to power the devices and to transmit the signals between devices.
U.S. Pat. No. 5,495,242 issued Feb. 27, 1996 to Kick et al. discloses a warning system for a hearing impaired automobile driver to detect a siren emitting sounds from a previously known category of siren sounds, and employing autocorrelation of digital signals to determine a repetitive pattern. However, an expensive digital signal processor is required for the autocorrelation and the device is not intended to detect high frequency beeps.
It would be desirable to have a portable, battery powered device which is responsive to certain types of audible alarm sounds and which will translate the alarm sounds into a form which may be heard by a person with high frequency hearing impairment.
Briefly stated, the invention comprises a battery-powered sonic relay, which is responsive to repetitive high frequency sonic pulses including at least the upper frequency range of human hearing, having logic means for determining that the repetitive pulses are occurring at a constant pulse repetition rate, and a sound producer responsive to the logic means adapted to produce sound predominately at low frequencies below those of the upper frequency range.
One version of the sonic relay employs pulse logic means adapted to provide a first logic signal when the sonic pulses occur at a constant repetition rate, and frequency filter means to provide a second logic signal when the sound frequencies are within the upper frequency range, the logic circuit being responsive to the first and second logic signals and providing an output signal to the sound producer.
Another embodiment of the invention uses a high pass filter with a signal detector to generate a digital signal in response to a sonic pulse within the upper frequency range, and a logic circuit comprising a microcontroller programmed to determine the start and end of such a sonic pulse and the interval until the start of the next such sonic pulse, and then provide an output to the sound producer if the pulses are occurring at a constant repetition rate.